Patients undergo collection of blood and urine samples at baseline and after completion of study therapy to assess pituitary function, thyroid function, and 24-hour urinary free cortisol levels. Additional assessments include corticotrophin-stimulation testing, dynamic pituitary function testing (i.e., arginine/growth-hormone releasing-hormone testing) to measure growth hormone secretion, and overnight 1 mg dexamethasone suppression testing to measure 8 a.m. serum cortisol levels. Patients also undergo MRI at baseline and after completion of study therapy to examine the effects of rosiglitazone maleate treatment on pituitary tumor size.